The present invention relates to an operational amplifier, and more particularly to stages of an operational amplifier including a class AB source follower output stage.
A conventional mixed mode integrated circuit system frequently uses different voltage supplies. Typically some analog signal processing, such as amplification, comparison, pulse generation, is performed at high voltage. A conventional operational amplifier that operates at high voltage (e.g., 14V) requires transistors and other devices that meet high voltage break down requirements, such as breakdown voltage of the drain with gate and source shorted to ground (BVDSS), breakdown voltage of the drain with gate shorted to ground and source floating (BVDSF), and breakdown, voltage of gate oxide layer (BVOX). Conventional operational amplifiers use transistors with breakdown voltages that can sustain a HV supply.
The present invention provides a folded cascode high voltage operational amplifier that may include in various aspects adaptive common input high voltage (HV) bias, adaptive push-pull source follower output HV bias, feed-forward slew rate enhancement, unaffected slew rate stability compensation, a combined split stability compensation, and a local power supply pre-filter.
In one aspect, an operational amplifier comprises a differential input stage that includes an adaptive high voltage differential pair for providing first and second output currents in response to first and second input voltage signals applied thereto. An intermediate bias stage provides at least one bias signal. An intermediate stage converts the first and second output currents into a first output signal in response to the at least one bias signal. An output stage includes a class AB source follower driver for generating a second output signal, in response to the first output signal.